Method of manufacturing aluminumcontaining alloys



Patented Dec. 16, 1941 METHOD OF MANUFACTURING ALUMINUM- CONTAININGALLOYS Victor 0. Allen, Madison, N. J., assignor to Wilbur B. DriverCompany, Newark, N. J., a. corporation of New Jersey No Drawing.Application June 25, 1940, Serial No. 342,269

3 Claims.

This invention relates to metallurgy and has for its object theprovision of an economically practical method of eliminating aluminumoxide, nitrid and hydride compounds from metallic alloys containing thesame. More particularly the invention relates to and has for its objectthe provision of an economically practical method of eliminatingaluminum oxide, nitride and hydride compounds from alloys consistingpredominately of one or more of the metals consisting of the group iron,nickel and copper and in lesser proportions one or more of the elementsMn, Si, Cr group metals, Zr group metals, V group metals, Co, Mg, rareearth group metals and the like, commonly associated therewith, with orwithout aluminum: in amounts ranging from fractional or substantiallyresidual percentages up to about 30%. Another object is to improve theductility and hot and cold workability of Al-containing alloys,particularly iron, nickel and copper alloys which either containaluminum in alloyed percentages or have been deoxidized and degasifiedby additions of aluminum, by eliminating therefrom aluminum oxide,nitride and hydride compounds. Other objects and advantages will beapparent as the invention is more fully hereinafter disclosed.

Aluminum is added to many alloys and especially to iron, nickel andcopper base alloys either as a deoxidizing and degasifying agent,

per se, or in alloyed amounts ranging from fractional percentages upwardto about 30% to impart thereto desired physical and chemical properties.In all such alloys, irrespective of associated metallic and metalloidconstituents, the chemical activity of the aluminum with resmall sizedwire and relatively thin sheet or strip form, particularly thoseutilized in the electrical industry for its magnetic or electricalresistance properties. Many of the alloy compositions heretoforeprepared are not obtainable in such form by known or by economicallypractical mechani- 4 cal deformation methods. I have discovered thatspect to oxygen, nitrogen and hydrogen is such I that substantially alloxide, nitride and hydride compounds present in the bath are convertedinto aluminum oxide, nitride and hydride compounds which are highlyrefractory and of low solubility' in the molten metal bath and which areof such low specific gravity that they are usually retained dispersed asrelatively small particles throughout the bath. g 1

Even when present in relatively small amounts these aluminum oxide,nitride and hydride-compounds have a marked deleterious effect upon thephysical properties of the solid metal and upon the grain growth andrecrystallization characterr istics of the same, which is most generallyreflected in the ductility and workability of the alloys.

' Many of the iron, nickel and copper base alloys containing aluminumare desired in relatively by eliminating aluminum oxide, nitride andhydride constituents from these said iron, nickel and copper base alloysthe hot and cold ductility and workability of the alloys are markedlyincreased and all such alloys that I so far have experimented with, whensubstantially free of such aluminum compounds, have been found to beamenable to mechanical deformation by economically practical methods tothe relatively thin wire, sheet or strip form desired with practicallyno difficulty and most of the alloys may be subjected to extensive coldmechanical deformation subsequently to hot deformation of the cast metalto condition the same for such cold working without developing excessiveamounts of work hardening strains seriously impairing the physicalproperties of the same.

Toaccomplish the elimination of aluminum oxide, nitride and hydridecompounds from molten metal baths, particularly molten iron, nickel andcopper base alloys containing aluminum, from substantially residualamounts to relatively large amounts approximating 30%, I have found thatthe molten metal 'bath must be vigorously agitated while in contact witha flux that is non-reducible or reactive with alumi.. num but reactivewith the said aluminum oxide, nitride and hydride compounds to decomposethe same forming compounds therewith that are either soluble in ormiscible with the said flux.

Flux materials that are non-reactive with aluminum falling generallywithin the scope of the present invention comprise alk'ali, alkalineearth, aluminum and ammonium halide and double halide compounds. Manydifferent combinations of these compounds are suitable for the purposeof the present invention and the selection of the same depends primarilyupon the temperature of the molten metal bath and the fluidity of theflux at that temperature. 'Additions of ammonium halide and doublehalide salts are eifective in increasing the fluidity of the flux and instabilizing the same against oxidation decomposition.

Materials falling generically within the scope of compounds reactivewith aluminum oxide, nitride and hydride compounds comprise any lithiumsalt or compound that is either soluble in or miscible with the fluxmixture employed. The lithium salt or compound is added to the flux insuch proportions relative to the volume of metal being treated and theknown amount of aluminum oxide, nitride and hydride compounds containedtherein, as will effect substantial elimination of these said aluminumcompounds within an economically practical time interval. Preferably,and in treating most metals, I employ a lithium halide compound, such aslithium fluoride. However, I have found that additions of lithium oxidealone or in addition to the halide (fluoride) compound are equally aseffective and, in the presence of excessive amounts of nitride andhydride compounds, are perhaps more eifective in the removal of the samethan is lithium fluoride alone.

As a specific embodiment of the practice of the present invention, I mayemploy cryolite as a flux and add thereto from 10 to 30% ,of lithiumfluoride or from 10 to 30% of a mixture of 90% lithium fluoride and 10%lithium oxide in the event the molten metal bath is more highlynitrogenized than usual. Alternatively, I may employ a mixture of sodiumand potassium chlorides or fluorides and incorporate therein 10 to 30%lithium fluoride or 10 to 30% of a mixture of 90% lithium fluoride and10% lithium oxide. A mixture of alkali and alkaline earth metalfluorides are equally as effective as a slag or flux and additions oflithium fluoride or of a mixture of lithium fluoride and oxide ashereinabove described will render the same reactive with the aluminumcompounds present in the molten metal bath.

In the practice of the present invention additions of lithium compoundsalone to the molten metal bath without any flux additions is effectiveto eliminate aluminum oxide, nitride and hydride compounds from thebath. However, in the absence of a flux means to dissolve or absorb ormix with the double Al.Li compounds formed, the elimination of the samefrom the molten metal bath will be difficult. Moreover, where the metalbath is being heated under more or less oxidizing conditions, extensivereoxidation of the bath is often obtained before cleansed metal may becast.

In the practice of the present invention, vigorous agitation of the bathand the lithium-containing flux contacting therewith is preferablyobtained by means of induced electric currents, as by this means thetemperature of the bath may at the same time be controlled andmaintained. However, alternatively I may employ any other type of meanseffective to obtain either emulsification of the flux in the metal bathor intimate association of the same with the metal sufiicient for thepurpose in view, as one skilled in the art Will perceive.

As a specific embodiment of the practice of the present invention theadaptation of the same to iron base alloys will be described;

Binary iron-aluminum alloys, for example alloys containing from 2 to 10%Al, have heretofore been proposed in the art for use as magnetic alloys.The magnetic permeability and watt loss in such alloys is directlyefiected by the amount of oxide, nitride and hydride compounds presenttherein, where all other associated metallic and non-metallic impuritieshave been substantially eliminated. Moreover, the presence of theseoxide, nitride and hydride compounds deleteriously effect the ductilityand workability of the alloys and also markedly influence the graingrowth and recrystallization properties of the same.

I have found that these alloys may be made substantially free fromaluminum oxide, nitride and hydride compounds by melting down the allayin an induction furnace of the Ajax-Northrup type and subjecting thealloy to treatment for a prolonged time interval with the reactive fluxcomposition of the present invention for a period of time eifective toremove therefrom the aluminum oxide, nitride and hydride compoundscontained therein. Preferably a flux consisting of cryolite containingabout 20% lithium fluoride is employed.

The resultant alloy product after casting will be found to besubstantially free from aluminum oxide, nitride and hydride compoundsand may be mechanically deformed to relatively thin sheet, strip or wireby subjecting the same first to hot mechanical deformation to conditionthe same for cold mechanical deformation, at a temperature approximating2000" F. to about 50% reduction in area, finishing at a temperature wellbelow its recrystallization temperature, which in most alloys willapproximate 1000 F. Thereafter the alloy may be subjected to coldmechanical deformation to final desired thickness or diameter, sheet,strip or wire without intermediate annealing.

The tertiary iron-chromium-aluminum alloys and the quaternaryiron-chromium-cobalt-alue minum alloys, heretofore proposed in the artfor use as electrical resistant alloys, when treated similarly also willevidence improved ductility and workability over those alloys not .sotreated, to such an extent that many of the alloys not heretoforeobtainable in fine wire or thin sheet or strip form may be so obtainedas a result of the practice of the present invention.

As an example, Fe.Cr.Al alloys containing 20% Cr, and from 3% to 10% Al,balance substantially all Fe, except for incidental and unavoidableimpurities, have been prepared and treated in accordance with thepresent invention and have been found on microscopical examination to beuniformly free from seams and stringers heretofore characterizing theuntreated alloys and have been found to evidence consistently markedlysuperior ductility and workability properties over those characteristicof the untreated alloys.

As an indication of the extent of improvement obtained, the 3% Al alloy(Cr 20%, bal. Fe) so treated as hereinabove described with lithiumfluoride-containing cryolite flux, when cast into an ingot 4"x4" andcogged at 2000 F. into a 2" x 2" billet finishing under 1500 F., wasfound to be substantially free from surface scams or stringerscharacteristic of such alloys not so treated. The billet when reheatedto 2000 F. and rolled on a falling temperature gradient to a 1%; inchrod finishing at a temperature under but approximating 1000 F. was foundto be capable of being subjected to cold mechanical deformation at roomtemperatures to wire size and additional cold drawing to .001 inch wirewithout intermediate annealing. The tensile strength of such cold drawnwire was found to be 85,700 p. s. i which is materially lower than anyheretofore obtained, the elongation was 24%. which was materially higherthan any heretofore obtained, and the electrical resistance was found tobe 650 ohms per c. m. f., a figure that is also materially higher thanthat obtained with similar alloys not so treated. Hardness testsindicated that the treated alloy was materially softer than theuntreated alloy, confirming the tensile and elongation tests abovegiven. The material above described has been cold fiat rolled from the1% inch rod to .010 inch strip size without intermediate anneaiing withcomparable results to the wire results above given.

Iron-chromium alloys containing 4, 6, 8 and 10% Al and 20% Cr were allcapable of extensive hot and cold mechanical deformation to relativelyand hydride impurities as contrasted to material not so treated.

One of the marked advantages obtained by the practice of the presentinvention is that th Alcontaining iron and iron-chromium alloys treatedin accordance with the present invention, even after prolonged heattreatment inducing recrystallization and grain growth in the coldmechanically deformed metal,'uniformly retain surprising ductility whichdifferentiates the metal from alloys not so treated.

Having hereinabove described the present invention generically andspecifically and given several specific embodiments and examples of thepractice of the same, it is believed apparent that many modificationsand adaptations may be made therein without essential departuretherefrom and all such are contemplated as may fall within the scope ofthe following claims.

What is claimed is:

1. The method of treating molten heavy metal baths to eflfect th removaltherefrom of aluminum oxide, nitride and hydride compounds, whichcomprises vigorously agitating the bath over an extended time intervalwhile in contact with a flux comprised of a mixture of alkali metal,alkaline earth metal and aluminum halide compounds non-reducible byaluminum, the major portion of said mixture consisting of compoundshaving a solubility towards aluminum oxide and the minor portion of saidmixture consisting of lithium compounds having a reactivity towardsaluminum nitride and hydride compounds and the total'amount of saidmixture relative to the mass of said molten metal being at leastsufficient to dissolve and react with substantially all of the aluminumoxide nitride and hydride compounds contained in said molten metal.

2. The method of claim 1, said major portion consisting of to cryoliteand said minor portion consisting of 10 to 30% of a mixture of lithiumfluoride and lithium oxide.

3. The method of claim 1, the said mixture consisting of from 70 to. 90%cryolite and from 10 to 30% of a lithium fluoride and lithium oxidemixture containing 90% lithium fluoride and 10% lithium oxide.

VICTOR O, ALLEN.

